The Spanish verb 'aplicar' (to apply) comes from the Latin word 'applicare', which meant 'to place near'. The Latin 'applicare' itself was formed by combining two elements: the prefix 'ad-' meaning 'toward' and the verb 'plicare' meaning 'to fold'. When 'ad-' came before 'plicare', the 'd' was assimilated to 'p' due to Latin phonetic rules, resulting in 'applicare'. Over time, as Latin evolved into Spanish, 'applicare' simplified to 'aplicar', losing one of its 'p's in the process.

Several common Spanish words share the same Latin root 'plicare' (to fold): 'plegar' (to fold), 'duplicar' (to duplicate), 'complicar' (to complicate), and 'explicar' (to explain). All these words maintain some connection to the original idea of folding - whether it's literally folding something, folding or doubling something to make a copy, making something complex by folding it many times, or unfolding (ex-) something to explain it.

English speakers will recognize many cognates of 'aplicar' that come from the same Latin source: 'apply', 'application', 'appliance'. The English word family also preserves other words with the 'plic-' root meaning 'to fold': 'complicate', 'duplicate', 'explicit', 'implicate', and 'replicate'. The connection between 'folding' and 'applying' might seem strange at first, but think of it as 'folding' something onto or toward something else.